The present invention generally relates to characteristic control systems for digital equalizers, and more particularly to a control system for a digital equalizer, in which one or a plurality of intermediate characteristics are set between first and second arbitrary characteristics when an equalizing characteristic of the digital equalizer is changed from the first arbitrary characteristic to the second arbitrary characteristic, to change the characteristic by successively obtaining the intermediate characteristic at each stage, and moreover, control is performed so that the change to each characteristic is performed with every lapse of a predetermined time, in order to prevent generation of noise and the like originated from the characteristic change of the digital equalizer when obtaining an analog signal by subjecting an output of the digital equalizer to a digital-to-analog conversion, so that the practicality of the digital equalizer is improved.
Conventionally, in systems for recording and reproducing digital pulse-modulated signals (such as a pulse code modulated signal), characteristic equalization for giving a predetermined amplitude or phase frequency characteristic was performed with respect to an analog signal obtained by subjecting a reproduced digital signal to a digital-to-analog conversion at a D/A converter. As another alternative, the characteristic equalization was performed with respect to a modulated signal of the digital pulse-modulated signal, that is, the original analog signal. The reason why the above method was employed is that the characteristic equalization could not be performed directly with respect to the digital signal, and only with respect to the analog signal.
Accordingly, even in a case of a digital signal obtained by high-quality recording, a signal processing such as passing the digital signal through a D/A converter was conventionally essential. Thus, degradation was introduced in the sound quality (if the input analog signal is an audio signal) when the digital signal passes through an analog system. In addition, there was a disadvantage in that the equalizer itself, which performs the characteristic equalization with respect to the analog signal, caused degradation in the sound quality.
Therefore, in order to prevent the above degradation in the sound quality, it was highly desirable to construct a digital equalizer capable of performing equalization of the amplitude and phase frequency characteristic of the converted analog output signal obtained from the digital signal, directly with respect to the digital signal. When realizing such a digital equalizer, it would be desirable to design the digital equalizer so that the characteristic equalized by the digital equalizer can be arbitrarily changed, and no noise is generated upon changing of the equalizing characteristic.